Place the cursor where you want the line
Type three hyphens and press Enter for a horizontal line
Type three underscores and press Enter for a thicker horizontal line
Type three asterisks and press Enter for a dotted line
Go to Insert
Select Shapes
Choose the Line tool
Click and drag to draw a line
Go to Home
Select Borders
Choose Bottom Border to add a line under text
Go to Insert
Select Table
Insert a one-cell table and adjust the border as needed